1. Field of the Invention
The present invention relates to a coaxial knob provided on an operating panel, for example, of an air conditioning apparatus and an acoustic apparatus, and more specifically, to a coaxial knob provided with an illuminating device for facilitating an operation thereof at night.
2. Prior Art
FIGS. 5 and 6 show a structure of a conventional coaxial knob 91 of this kind. For example, in the case of an acoustic apparatus, a variable resistor 20 including an outer shaft 21 having a resistance control function and an inner shaft 22 having a switch function is very often employed.
In this case, an outer knob 92 with an index 92a showing a degree of adjustment, for example, such as an arrow, is mounted on the outer shaft 21, and an inner knob 93 with an index 93a showing a switch function, for example, such as "ON", is mounted on the inner shaft 22. A panel surface 23 is provided with a graduation 23a thereon to indicate the adjusted state. When use is expected at night or at dark places, the aforesaid panel surface 23 is made of a double configuration comprising, for example, a transparent member for the graduation 23a and an opaque member for the other member. A light source 24 disposed on the back of the panel surface 23 is lit to effect illumination so that the apparatus can be used at night.
However, in the above-described conventional apparatus, the graduation 23a can be certainly read at night but the index 92a or 93a to be matched thereto is never illuminated and therefore cannot be read. Thus, the aforementioned apparatus is not completely suitable for use at night, thus posing difficulties in the operation of apparatus at night.